Nobuko Maeda

Bacterial Interactions in Dental Biofilm Development

Recent analyses with ribosomal RNA-based technologies have revealed the diversity of bacterial populations within dental biofilms, and have highlighted their important contributions to oral health and disease. Dental biofilms are exceedingly complex and multispecies ecosystems, where oral bacteria interact cooperatively or competitively with other members. Bacterial interactions that influence dental biofilm communities include various different mechanisms. During the early stage of biofilm formation, it is known that planktonic bacterial cells directly attach to surfaces of the oral cavity or indirectly bind to other bacterial cells that have already colonized. Adherence through co-aggregation may be critical for the temporary retention of bacteria on dental surfaces, and may facilitate eventual bacterial colonization. It is likely that metabolic communication, genetic exchange, production of inhibitory factors (e.g., bacteriocins, hydrogen peroxide, etc.), and quorum-sensing are pivotal regulatory factors that determine the bacterial composition and/or metabolism. Since each bacterium can easily access a neighboring bacterial cell and its metabolites, genetic exchanges and metabolic communication may occur frequently in dental biofilms. Quorum-sensing is defined as gene regulation in response to cell density, which influences various functions, e.g., virulence and bacteriocin production. In this review, we discuss these important interactions among oral bacteria within the dental biofilm communities.

Distribution of Salivary Lactobacillus and Bifidobacterium Species in Periodontal Health and Disease

We surveyed the distribution of salivary Lactobacillus and Bifidobacterium species in periodontitis patients and healthy subjects. Approximately 700 lactobacilli and 300 bifidobacterial isolates were obtained from 16 young, orally healthy subjects (mean age ± standard deviation: 21.0±2.0 y), 16 periodontitis patients (51.6±13.8 y), and 14 well-maintained former periodontitis patients (60.2±9.6 y). Among eleven Lactobacillus species detected in saliva, L. salivarius, L. gasseri, and L. fermentum were prevalent, but no species was specifically associated with periodontal health. In contrast, of four Bifidobacterium species, B. adolescentis was specifically (P<0.05) prevalent in young healthy subjects compared with the other two groups. Furthermore, the bifidobacterial count of the well-maintained subjects was the highest (P<0.05) among the groups. These results suggest that bifidobacterial count and species might be associated with periodontal health status and/or age.

One-Stage Full-Mouth Versus Partial- Mouth Scaling and Root Planing During the Effective Half-Life of Systemically Administered Azithromycin

BACKGROUND One-stage full-mouth scaling and root planing (FM-SRP) in combination with systemically administered azithromycin was shown to be clinically and bacteriologically effective in the treatment of chronic periodontitis. However, FM-SRP requires 2 hours for completion. Azithromycin has a long half-life. Therefore, if SRP of the full mouth is performed within 7 days while an effective concentration of azithromycin remains in the gingiva, the effects may be the same as FM-SRP. The aim of this study was to compare the clinical and bacteriologic effects of FM-SRP and partial-mouth scaling and root planing (PM-SRP) in patients with chronic periodontitis, which was performed in three sessions within 7 days, during the effective half-life of systemically administrated azithromycin. METHODS Thirty adult subjects with chronic periodontitis were randomly divided into three groups (FM-SRP, PM-SRP, and control). A clinical examination was conducted to record the probing depth, clinical attachment level gain, bleeding on probing, gingival index, and volume of gingival crevicular fluid; bacterial samples were obtained before treatment and 1, 3, 6, 9, and 12 months thereafter. Quantitative and qualitative analyses were performed using the polymerase chain reaction-Invader method. RESULTS All clinical parameters showed better improvement in FM-SRP and PM-SRP groups compared to the control group, with no significant differences between the two test groups. Periodontal bacteria were well controlled in the two test groups, but they tended to increase gradually 3 months after treatment in the control group. CONCLUSION PM- and FM-SRP demonstrated comparable clinical and bacteriologic results.

Abscess Forming Ability of Streptococcus milleri Group: Synergistic Effect with Fusobacterium nucleatum

The abscess forming abilities of “Streptococcus milleri” strains (Streptococcus constellatus, Streptococcus anginosus, and Streptococcus intermedius) isolated from dentoalveolar abscesses and the synergistic effect of Fusobacterium nucleatum co‐inoculated with the isolates were examined on a mouse subcutaneous abscess model. Five days after inoculation, all S. milleri strains formed abscesses, which showed less pathological spread to surrounding connective tissues than those formed by Staphylococcus aureus 209P strain and were similar to those by F. nucleatum ATCC25586. When each S. milleri strain and F. nucleatum were co‐inoculated, abscess sizes and each bacterial number recovered from abscesses increased in comparison to those treated by bacterial mono‐inoculation of each S. milleri strain or F. nucleatum alone. The strongest synergistic effect was observed in the combination of S. constellatus and F. nucleatum. In a time course experiment with this combination, the recovery of S. constellatus subsequently decreased after the decrement of F. nucleatum, and it appeared that the association with F. nucleatum maintained the bacterial number of S. constellatus in the abscess. The cell‐free supernatant of F. nucleatum had a tendency to increase the abscess size caused by S. constellatus in this model. When S. constellatus was cultured with F. nucleatum culture supernatant in vitro, growth enhancement in the early phase was observed. Furthermore, the phagocytic killing of S. constellatus by human polymorphonuclear leukocytes (PMNs) was significantly suppressed and the PMN membranes appeared to be injured by addition of the F. nucleatum culture supernatant. These results suggest that the pathogenicity of S. milleri strains in odontogenic infections may be enhanced by the co‐existence of F. nucleatum.

Incidence of Prevotella intermedia and Prevotella nigrescens in periodontal health and disease.

The incidence of black‐pigmented rods (BPRs), especially Prevotella intermedia and Prevotella nigrescens, in periodontal health and disease were examined. Furthermore, the degradative enzyme activities of P. intermedia were compared among the strains from periodontal health and disease. Microbiological specimens were collected from subgingival crevice or periodontal pocket by paper point. The BPRs were found in 71.1% of periodontally healthy subjects (n = 45), and in 47.1% of healthy sites (n = 34) and 87.8% of active sites (n = 41) among periodontally diseased patients. Porphyromonas gingivalis was detected only in active sites of periodontally diseased patients (17.8% of 180 strains). P. intermedia was the predominant BPR in both healthy and active sites (37.3 and 41.7%, respectively) of the patients. However, P. nigrescens was the predominant BPR (70.5% of 173 strains) in periodontally healthy subjects. The enzyme activities of esterase, esterase‐lipase, acid‐phosphatase and α‐fucosidase of P. intermedia strains isolated from active sites in patients were significantly higher (P < 0.05) than those of healthy subjects. The results suggest that P. intermedia might increase the activity of degradative enzymes under a certain condition and support the progression of periodontitis.

Interactions between salivary Bifidobacterium adolescentis and other oral bacteria : in vitro coaggregation and coadhesion assays

Coaggregation assays were performed to investigate interactions between oral Bifidobacterium adolescentis and other oral bacterial species. Bifidobacterium adolescentis OLB6410 isolated from the saliva of healthy humans did not coaggregate with Actinomyces naeslundii JCM8350, Streptococcus mitis OLS3293, Streptococcus sanguinis JCM5708, Veillonella parvula ATCC17745 or Porphyromonas gingivalis OB7124, but it did coaggregate with Fusobacterium nucleatum JCM8532. Subsequent examination of biofilm formation on saliva-coated hydroxyapatite discs using FISH revealed that B. adolescentis OLB6410 could not directly adhere to the coated discs. It did, however, adhere to biofilms of A. naeslundii, V. parvula, and F. nucleatum, although it did not coaggregate with A. naeslundii nor with V. parvula. These results suggest that the adhesion of B. adolescentis to tooth surfaces is mediated by other oral bacteria. Heat- or proteinase K-treated F. nucleatum could not coaggregate with B. adolescentis. Similarly, the coaggregation and coadhesion of proteinase K-treated B. adolescentis were strongly inhibited. It is therefore probable that proteinaceous factors on the cellular surface of B. adolescentis and F. nucleatum are involved in their interaction. The data presented in this study add to our understanding of bifidobacterial colonization in the human oral cavity.

Reduction of vitamin K concentration by salivary Bifidobacterium strains and their possible nutritional competition with Porphyromonas gingivalis

Aims:  To assess the possibility that bifidobacteria compete with Porphyromonas gingivalis for their mutual growth factor vitamin K. This study also examined whether salivary Bifidobacterium species decrease vitamin K concentration in the growth medium.

Isolation of bacteria from cervical lymph nodes in patients with oral cancer

Thirty patients with oral mucosal cancer were studied in relation to oral mucosal damage and bacterial translocation to the regional lymph nodes in the neck. All 30 patients (gingiva 11, tongue 13, cheek mucosa four, oral floor two) underwent extensive, clean-contaminated, head-and-neck surgery (including neck dissection) with free flap reconstruction. A total of 153 lymph nodes was harvested for microbial and histological examination. Viable bacteria were isolated from 70 lymph nodes (45.8%) from 25 patients (83.3%). Bacterial cells in the nodes were detected by scanning electron microscopy. Bacterial translocation was found more often in metastatic nodes (75.0%) than in uninvolved nodes (40.3%) (p = 0.015; chi2 test). Gingival carcinoma yielded 56.4% of bacterial growth in the regional lymph nodes compared to tongue (40.3%), oral floor (40.0%) and cheek mucosa (37.5%). As the gingival carcinoma group includes more T4 cases (11/11; 100%) than the other three groups (7/19; 36.8%), bacterial translocation in uninvolved nodes could be caused by the size and invasion of the primary oral tumor. Oral streptococci (Streptococcus intermedius, Strep. constellatus, Strep. oralis, Strep. mitis, Strep. sanguis, Strep. salivarius) were the most common isolates. Aerobic enteric bacteria (Enterococcus, Escherichia, Klebsiella etc.) were also found in the lymph nodes. Among the anaerobic bacteria, Peptostreptococcus spp. were isolated from 12 patients. Damaged oral mucosa in patients with oral cancer might allow the new bacterial colonization on the surface and subsequently drain the bacteria into the regional lymph nodes as well as the general circulation.

Bifidobacterium tsurumiense sp. nov., from hamster dental plaque.

Three novel micro-organisms, designated strains OMB115(T), OMB118 and OMB120, were isolated from dental plaque from golden hamsters fed with a high-carbohydrate diet. The three strains were Gram-positive, facultatively anaerobic rods that lacked catalase activity. Analysis of their partial 16S rRNA gene sequences indicated that these isolates belonged to the genus Bifidobacterium. They grew under aerobic conditions and each had a DNA G+C content of 53 mol%. On the basis of phylogenetic analyses involving phenotypic characterization and partial 16S rRNA gene sequencing, strain OMB115(T) represents a novel species of the genus Bifidobacterium, for which the name Bifidobacterium tsurumiense sp. nov. is proposed. The type strain is OMB115(T) (=JCM 13495(T) =DSM 17777(T)).

Metascardovia criceti Gen. Nov., Sp. Nov., from hamster dental plaque.

A novel microorganism, Metascardovia criceti gen. nov., sp. nov., was isolated from dental plaque of golden hamsters fed with a high‐carbohydrate diet. The three isolated strains, OMB104, OMB105, and OMB107, were Gram‐positive, facultative anaerobic rods that lacked catalase activity. Analyses of the partial 16S rRNA and heat‐shock protein 60 (HSP60) gene sequences of these isolates indicated that they belonged to the family Bifidobacteriaceae. However, in contrast to Bifidobacterium, one of the genera under this family, these isolates grew under aerobic conditions, and the DNA G + C contents were lower (53 mol%) than those of Bifidobacterium. On the basis of phylogenetic analyses using phenotypic characterization, and partial 16S rRNA and HSP60 gene sequences data, we propose a novel taxa, Metascardovia criceti for OMB105T (type strain=JCM 13493T=DSM 17774T) for this newly described isolate.